Acidproof, hydrolysis-resistant optical and ophthalmic glass of low density

ABSTRACT

An optical and ophthalmic glass having an index of refraction of ≧1.69, an Abbe number of ≧37, and a density of ≦3.30 g/cm 3 , consists essentially of (in % by weight): 
     
         ______________________________________                                    
 
    
     SiO 2                   18-36                                          
B 2  O 3             3-18                                           
GeO 2                   0-8                                            
Al 2  O 3            0-6,                                           
wherein SiO 2  + B 2  O 3  + Al 2  O 3  + GeO 2         
                           25-39                                          
P 2  O 5              0-14,                                         
wherein SiO 2  + B 2  O 3  + Al 2  O 3  + GeO 2  +      
P 2  O 5  =          30-44                                          
Li 2  O                 0-12                                           
Na 2  O                 0-14                                           
K 2  O                  0-18                                           
Li 2  O + Na 2  O + K 2  O =                                     
                           2-18                                           
MgO                        0-15                                           
CaO                        7-25                                           
MgO + CaO                  15-32                                          
SrO                        0-13                                           
BaO                        0-17                                           
ZnO                        0-15                                           
PbO                        0-10                                           
SrO + BaO + ZnO + PbO      0-20                                           
TiO 2                   3-14                                           
Nb 2  O 5            0-13                                           
WO 3                    0-10                                           
TiO 2  + Nb 2  O 5  + WO 3  =                                 
                           10-21                                          
ZrO 2                    0-15,                                         
La 2  O 3            0-20                                           
Y 2  O 3             0-16                                           
Gd 2  O 3            0-16                                           
Yb 2  O 3            0-10                                           
La 2  O 3  + Y 2  O 3  + Gd 2  O 3  + Yb 2  O 3   
=                          0-20                                           
Ta 2  O 5            0-13                                           
HfO 2                   0-5                                            
SnO 2                   0-6.                                           
______________________________________

BACKGROUND OF THE INVENTION

The present invention relates to a lightweight, acidproof,hydrolysis-resistant optical and ophthalmic glass having an index ofrefraction n_(d) ≧1.69, an Abbe number v_(d) ≧37, and a density s≦3.30g/cm³. It is a borosilicate glass in the system SiO₂ -B₂ O₃ -CaO-TiO₂.

Lightweight glasses of a high refractive index, for example forophthalmic optics or for optical systems have been described in DAS[German Published Application] No. 2,259,183. These glasses, having adensity of about 3.0 g/cm³, are especially well suited for strongcorrections, but exhibit the grave disadvantage of strong dispersion,i.e., they have a comparatively low Abbe number ≦33. This strongdispersion causes a person wearing glasses of this type to seepronounced color fringes. For this reason, attempts have been made toimprove their dispersion while retaining the same or only a slightlyincreased specific density (French Pat. No. 2,427,309). These newglasses, however, also fail to meet the requirements for a v_(d) value≧37 which generally would be highly desirable.

In further developments, glasses were provided having an increased Abbenumber; however, they cannot be manufactured continuously due to theirinstability toward crystallization. In addition, their chemicalresistance (acidproofness and resistance to climatic changes) do notsatisfy the requirements imposed on spectacle lenses. Glasses of thistype are described in DOS [German Unexamined Laid-Open Application] No.2,809,409 and DAS No. 2,715,894, as well as DAS No. 2,623,683.

Accordingly, it is an object of the present invention to provide a newoptical and ophthalmic glass which meets the aforementioned requirementsand avoids the aforementioned disadvantages.

Upon further study of the specification and appended claims, furtherobjects and advantages of this invention will become apparent to thoseskilled in the art.

These objects have been attained by providing an optical and ophthalmicglass having an index of refraction of ≧1.69, (e.g., 1.69-1.71), an Abbenumber of ≧37, (e.g., 37-43) and a density of ≦3.30 g/cm³, (e.g.,3.30-3.10), comprising (in % by weight):

    ______________________________________                                                             Preferred Range,                                                    General Range                                                                           When Included                                            ______________________________________                                        SiO.sub.2    18-36       18-36                                                B.sub.2 O.sub.3                                                                            3-18        3-18                                                 GeO.sub.2    0-8         0-8                                                  Al.sub.2 O.sub.3                                                                            0-6,       0-6                                                  wherein SiO.sub.2 + B.sub.2 O.sub.3 + Al.sub.2 O.sub.3 + GeO.sub.2 =          25-39                                                                         P.sub.2 O.sub.5                                                                             0-14,      0.5-4                                                wherein SiO.sub.2 + B.sub.2 O.sub.3 + Al.sub.2 O.sub.3 + GeO.sub.2 +          P.sub.2 O.sub.5 = 30-44                                                       Li.sub.2 O   0-12        0-12                                                 Na.sub.2 O   0-14        0-14                                                 K.sub.2 O    0-18        0-18                                                 Li.sub.2 O + Na.sub.2 O + K.sub.2 O = 2-18                                                         2-18                                                     MgO          0-15        0-15                                                 CaO          7-25        7-25                                                 MgO + CaO    15-32       15-32                                                SrO          0-13        0-13                                                 BaO          0- 17       0-17                                                 ZnO          0-15        0-15                                                 PbO          0-10        0-10                                                 SrO + BaO + ZnO + PbO 0-20                                                    TiO.sub.2    3-14        3-14                                                 Nb.sub.2 O.sub.5                                                                           0-13        0-13                                                 WO.sub.3     0-10        0-10                                                 TiO.sub.2 + Nb.sub.2 O.sub.5 + WO.sub.3 = 10-21                               ZrO.sub.2     0-15,      3-8                                                  La.sub.2 O.sub.3                                                                           0-20        3-12                                                 Y.sub.2 O.sub.3                                                                            0-16        0-16                                                 Gd.sub.2 O.sub.3                                                                           0-16        0-16                                                 Yb.sub.2 O.sub.3                                                                           0-10        0-10                                                 La.sub.2 O.sub.3 + Y.sub.2 O.sub.3 + Gd.sub.2 O.sub.3 +                       Yb.sub.2 O.sub.3 =  0-20                                                                           3-12                                                     Ta.sub.2 O.sub.5                                                                           0-13        0-13                                                 HfO.sub.2    0-5         0-5                                                  SnO.sub.2     0-6.       0-6                                                  ______________________________________                                    

A particularly preferred such glass has a v_(d) value of ≧39 and adensity s of ≦3.2 g/cm³, is sufficiently stable with respect tocrystallization to permit continuous manufacture and simultaneouslysatisfies the minimum requirements for acid resistance and resistanceagainst climatic changes, and comprises (% by weight):

    ______________________________________                                                B.sub.2 O.sub.3                                                                            5-14                                                             SiO.sub.2    24-32                                                            Al.sub.2 O.sub.3                                                                           0-6                                                              GeO.sub.2    0-8                                                              B.sub.2 O.sub.3 + SiO.sub.2 + Al.sub.2 O.sub.3 + GeO.sub.2 =                  33-39                                                                         P.sub.2 O.sub.5                                                                            0-6                                                              B.sub.2 O.sub.3 + SiO.sub.2 + Al.sub.2 O.sub.3 + GeO.sub.2 +                  P.sub.2 O.sub.5 = 37-43                                                       Li.sub.2 O   0-7                                                              Na.sub.2 O   0-8                                                              K.sub.2 O    0-11                                                             Li.sub.2 O + Na.sub.2 O + K.sub.2 O = 4-14                                    MgO          0-10                                                             CaO          12-25                                                            MgO + CaO = 18-27                                                             ZnO          0-8                                                              BaO          0-6                                                              SrO          0-6                                                              PbO          0-5                                                              ZnO + BaO + SrO + PbO = 0-8                                                   TiO.sub.2    6-10                                                             Nb.sub.2 O.sub.5                                                                           0-8                                                              WO.sub.3     0-10                                                             TiO.sub.2 + Nb.sub.2 O.sub.5 + WO.sub.3 = 13-19                               ZrO.sub.2    3-9                                                              La.sub.2 O.sub.3                                                                           0-11                                                             Y.sub.2 O.sub.3                                                                            0-12                                                             Gd.sub.2 O.sub.3                                                                           0-8                                                              Yb.sub.2 O.sub.3                                                                           0-7                                                              La.sub.2 O.sub.3 + Y.sub.2 O.sub.3 + Gd.sub.2 O.sub.3 + Yb.sub.2              O.sub.3 = 0-14                                                                Ta.sub.2 O.sub.5                                                                           0-7                                                              HfO.sub.2    0-6                                                              SnO.sub.2    0-6                                                      ______________________________________                                    

DETAILED DISCUSSION

The present invention makes it possible to continuously producespectacle glass and optical glasses with adequate chemical resistance(e.g., acidproofness and water resistance), with an index of refractionof about 1.7 and an Abbe number ≧37, at a density of ≦3.30 g/cm³ ; atthe same time, fusion with commercial spectacle crown glass can beensured by setting its expansion coefficient α(20-300)·10⁻⁷ at 90-98,e.g., by conventional selection of suitable amounts of the followingingredients: Na₂ O, K₂ O, Li₂ O.

According to this invention, a borosilicate glass is chosen as the basicglass system. As is known, this particular one has an excellently highchemical resistance. This basic glass system is combined with componentsincreasing the refractive index, primarily, the light alkaline earthmetal oxides MgO and CaO, especially CaO, and with components greatlyraising the index of refraction while not impairing the Abbe number tooextensively, i.e., Nb₂ O₅ and TiO₂ as well as ZrO₂. In order tostabilize this system against reseparation, an addition of alkali metaloxide is necessary.

It has been found that this system, which is only moderately stable withrespect to devitrification and which also exhibits insufficient chemicalresistance due to its high content of alkaline earth metal oxides aswell as alkali metal oxides, can be improved with regard to bothaforementioned properties--devitrification stability and chemicalresistance--if P₂ O₅ is added thereto.

The glass according to this invention is made up of the followingcomponents in the recited ranges (in % by weight):

    ______________________________________                                                SiO.sub.2                                                                           18-36                                                                   B.sub.2 O.sub.3                                                                      3-18                                                                   GeO.sub.2                                                                           0-8                                                                     Al.sub.2 O.sub.3                                                                    0-6                                                             ______________________________________                                    

wherein the sum total of these tri- and tetravalent vitrifying agentsamounts to 25-39% by weight.

As indicated above, the devitrification stability can be improved, alongwith the chemical resistance, by adding the pentavalent vitrifying agentP₂ O₅ ; for this reason, an addition of a few percent of P₂ O₅ isuseful. An addition of >14%, however, renders the glass unstable againstdevitrification. Preferred is 0.5-4.0% of P₂ O₅. The sum total of thetri- and tetravalent vitrifying agents plus P₂ O₅ amounts to 30-44% byweight.

As mentioned, the addition of an alkali metal is required to preventdemixing. This can be achieved by the following additions:

    ______________________________________                                                         % by Weight                                                  ______________________________________                                        Li.sub.2 O         0-12                                                       Na.sub.2 O         0-14                                                       K.sub.2 O          0-18                                                       Li.sub.2 O + Na.sub.2 O + K.sub.2 O =                                                            2-18                                                       ______________________________________                                    

If the proportion of alkali metal oxides >18%, devitrification stabilityand chemical resistance are negatively affected.

CaO is added as an essential component. It achieves a marked rise in theindex of refraction, while ensuring a high Abbe number andsimultaneously maintaining a low density. The function of the CaO canalso be coachieved per the following by MgO within relatively widelimits. The proportions of the light alkaline earth metal oxides MgO andCaO are:

    ______________________________________                                                    % by Weight                                                       ______________________________________                                        MgO           0-15                                                            CaO           7-25                                                            MgO + CaO =   15-32                                                           ______________________________________                                    

From the heavy alkaline earth metal oxides SrO and BaO, the followingproportions can be added, if necessary, e.g., in order to adjust thedensity:

    ______________________________________                                        SrO               0-13% by weight                                             BaO               0-17% by weight;                                            ______________________________________                                    

furthermore permissible are:

    ______________________________________                                        ZnO               0-15% by weight                                             PbO               0-10% by weight,                                            ______________________________________                                    

with the condition: SrO+BaO+ZnO+PbO≦20%, since the density increasesgreatly at larger proportions.

Another absolutely necessary component of the glass of this invention isTiO₂ since, as is known, the index of refraction is thereby greatlyraised while the density increases by only a small amount. An additionof 3-14% by weight is required to raise the index of refraction to thedesired value of >1.69. Another positive property added by TiO₂ is animprovement in chemical resistance.

Similar effects as for TiO₂ are exhibited by Nb₂ O₅ and WO₃. Theseoxides can be added in amounts of

    ______________________________________                                        Nb.sub.2 O.sub.5  0-13% by weight                                             WO.sub.3          0-10% by weight                                             ______________________________________                                    

The sum total of these three oxides TiO₂, Nb₂ O₅, WO₃, similar inproperties, is 10-21% by weight.

Another usable oxide is ZrO₂. This compound greatly increases the indexof refraction, but reduces the Abbe number only moderately, whileimproving the chemical resistance to a marked extent. This oxide can beadded in proportions of 0-15% by weight; a proportion of 3-9% by weightis preferred.

To stabilize the glass further against devitrification, the followingcan be added per this invention:

    ______________________________________                                        La.sub.2 O.sub.3  0-20% by weight                                             Y.sub.2 O.sub.3   0-16% by weight                                             Gd.sub.2 O.sub.3  0-16% by weight                                             Yb.sub.2 O.sub.3  0-10% by weight                                             Total             0-20% by weight                                             ______________________________________                                    

Furthermore, an addition of 0-13% Ta₂ O₅ is possible. HfO₂ can be addedin amounts of 0-5% by weight, and also SnO₂ in 0-6% by weight. Theseions are added for purposes of adjusting the index of refraction.

A portion of the oxygen ions (e.g., 0-1% by weight) can be replaced byfluoride ions by introducing a fluoride into the glass melt instead ofan oxide. Fluoride ions may be added for the purpose of decreasing themelting temperature and stabilizing the glass against devitrification.

    ______________________________________                                        EXAMPLE OF A MELT                                                             Glass batch charged for 220 Kg of glass                                       % by Weight  Raw Material                                                                              Weighed Quantity in kg                               ______________________________________                                        B.sub.2 O.sub.3                                                                     11.25      H.sub.3 BO.sub.3                                                                          43.88                                            SiO.sub.2                                                                           24.00      SiO.sub.2   52.88                                            P.sub.2 O.sub.5                                                                     3.10       P.sub.2 O.sub.5                                                                            6.82                                            Li.sub.2 O                                                                          0.70       Li.sub.2 CO.sub.3                                                                          3.85                                            Na.sub.2 O                                                                          4.50       Na.sub.2 CO.sub.3                                                                         17.00                                            K.sub.2 O                                                                           4.55       K.sub.2 CO.sub.3                                                                          14.70                                            MgO   2.90       MgCO.sub.3  15.08                                            CaO   16.30      CaCO.sub.3  63.26                                            La.sub.2 O.sub.3                                                                    6.60       La.sub.2 O.sub.3                                                                          14.55                                            TiO.sub.2                                                                           9.00       TiO.sub.2   19.82                                            ZrO.sub.2                                                                           1.65       ZrO.sub.2    3.65                                            Nb.sub.2 O.sub.5                                                                    2.60       Nb.sub.2 O.sub.5                                                                           5.72                                            Ta.sub.2 O.sub.5                                                                    12.85      Ta.sub.2 O.sub.5                                                                          28.30                                            ______________________________________                                    

The individual oxides can also be introduced in complex form, forexample P₂ O₅ bound to the alkali or alkaline earth oxides, e.g., asCaPO₃ or Ca₂ P₂ O₇. It is also possible, for example, to use SiO₂ inpart as CaSiO₃ or, for example, as ZrSiO₄ with appropriatestoichiometric conversion. It is likewise feasible to introduce smallamounts of a fluoride, e.g., as an alkali metal, alkaline earth metal,or rare earth fluoride. As₂ O₃ or Sb₂ O₃ is added to the batch as therefining agent (e.g., in amounts of 0.1-1% by weight); then the batch ismixed thoroughly and melted at approximately 1400° C. in a Pt crucibleor a ceramic trough within about 8 hours. After a refining time of about3 hours, the batch is stirred until the discharge or pouring temperaturehas been reached. The glass is conventionally either poured into castingmolds or press-molded. The glass of this invention is particularlyuseful as spectacle glass requiring strong correction.

Without further elaboration, it is believed that one skilled in the artcan, using the preceding description, utilize the present invention toits fullest extent. The following preferred specific embodiments are,therefore, to be construed as merely illustrative, and not limitative ofthe remainder of the disclosure in any way whatsoever. In the followingexamples, all temperatures are set forth uncorrected in degrees Celsius;unless otherwise indicated, all parts and percentages are by weight.

                                      TABLE                                       __________________________________________________________________________    (Examples in % by Weight)                                                     __________________________________________________________________________        1    2    3    4    5    6    7                                           __________________________________________________________________________    B.sub.2 O.sub.3                                                                   3.20 17.75                                                                              9.10 9.50 12.95                                                                              10.25                                                                              9.80                                        SiO.sub.2                                                                         34.80                                                                              18.60                                                                              21.60                                                                              24.00                                                                              25.55                                                                              22.80                                                                              21.60                                       Al.sub.2 O.sub.3                                                                  --   --   --   --   --   5.10 --                                          GeO.sub.2                                                                         --   --   --   --   --   --   --                                          P.sub.2 O.sub.5                                                                   --   1.80 --   1.30 4.75 --   7.10                                        Li.sub.2 O                                                                        2.07 1.15 --   --   9.15 1.45 1.10                                        Na.sub.2 O                                                                        0.70 3.15 --   12.10                                                                              --   3.00 2.30                                        K.sub.2 O                                                                         6.50 4.80 17.15                                                                              --   --   4.60 4.65                                        MgO 3.75 6.20 5.45 5.85 5.00 5.95 6.50                                        CaO 11.90                                                                              15.70                                                                              17.00                                                                              16.30                                                                              14.90                                                                              16.50                                                                              16.00                                       SrO --   --   --   --   --   --   --                                          BaO --   --   --   --   2.15 --   --                                          ZnO --   2.05 1.85 2.00 2.25 2.00 2.00                                        PbO --   --   --   --   --   --   --                                          La.sub.2 O.sub.3                                                                  19.88                                                                              7.50 7.30 7.90 --   8.00 8.10                                        Y.sub.2 O.sub.3                                                                   --   --   --   --   --   --   --                                          Gd.sub.2 O.sub.3                                                                  --   --   --   --   --   --   --                                          Y.sub.2 O.sub.3                                                                   --   --   --   --   --   --   --                                          TiQ.sub.2                                                                         7.80 8.15 9.00 8.70 8.90 7.80 7.95                                        ZrO.sub.2                                                                         5.70 6.30 5.55 6.00 6.90 6.00 6.15                                        Nb.sub.2 O.sub.5                                                                  3.70 6.85 6.00 6.35 7.50 6.55 6.75                                        WO.sub.3                                                                          --   --   --   --   --   --   --                                          Ta.sub.2 O.sub.5                                                                  --   --   --   --   --   --   --                                          nd  1.6990                                                                             1.6982                                                                              1.6920                                                                            1.6943                                                                             1.7026                                                                             1.6977                                                                             1.6949                                      νd                                                                             40.5 39.5 38.6 38.5 39.9 39.2 39.3                                        S   3.30 3.14 3.12 3.16 3.02 3.15 3.17                                        __________________________________________________________________________        8    9    10   11   12   13   14                                          __________________________________________________________________________    B.sub.2 O.sub.3                                                                   7.85 11.45                                                                              12.50                                                                              11.20                                                                              11.60                                                                              11.35                                                                              11.35                                       SiO.sub.2                                                                         29.50                                                                              25.80                                                                              25.80                                                                              25.00                                                                              26.00                                                                              26.15                                                                              25.40                                       Al.sub.2 O.sub.3                                                                  --   --   --   --   --   --   --                                          GeO.sub.2                                                                         --   --   --   --   --   --   --                                          P.sub.2 O.sub.5                                                                   1.45 --   --   --   --   --   --                                          Li.sub.2 O                                                                        1.40 1.50 1.50 1.40 2.90 --   1.40                                        Na.sub.2 O                                                                        2.90 3.10 3.10 2.90 3.00 5.90 3.00                                        K.sub.2 O                                                                         4.40 4.75 4.70 4.40 --   4.50 4.50                                        MgO --   14.25                                                                              0.50 5.70 5.90 3.85 5.80                                        CaO 19.80                                                                              7.05 24.75                                                                              7.90 11.00                                                                              8.70 14.70                                       SrO --   --   --   12.10                                                                              --   --   --                                          BaO 3.60 --   --   --   16.80                                                                              --   --                                          ZnO --   2.05 0.60 1.90 --   14.60                                                                              1.95                                        PbO --   --   --   --   --   --   9.60                                        La.sub.2 O.sub.3                                                                  13.70                                                                              8.20 6.55 7.65 --   5.20 --                                          Y.sub.2 O.sub.3                                                                   --   --   --   --   --   --   3.60                                        Gd.sub.2 O.sub.3                                                                  --   --   --   --   --   --   --                                          Yb.sub.2 O.sub.3                                                                  --   --   --   --   --   --   --                                          TiO.sub.2                                                                         6.35 8.05 7.95 7.50 10.20                                                                              7.60 7.15                                        ZrO 2.90 7.00 6.10 5.80 6.00 5.90 5.80                                        Nb.sub.2 O.sub.5                                                                  6.15 6.80 5.95 6.55 6.60 6.25 5.75                                        WO.sub.3                                                                          --   --   --   --   --   --   --                                          Ta.sub.2 O.sub.5                                                                  --   --   --   --   --   --   --                                          nd  1.6991                                                                             1.7051                                                                             1.7005                                                                             1.7000                                                                             1.7075                                                                             1.6982                                                                             1.7064                                      νd                                                                             41.6 38.1 40.5 40.0 38.3 38.5 37.10                                       S   3.29 3.17 3.12 3.30 3.29 3.26 3.25                                        __________________________________________________________________________        15   16   17   18   19   20   21                                          __________________________________________________________________________    B.sub.2 O.sub.3                                                                   7.75 8.10 11.20                                                                              11.60                                                                              11.25                                                                              9.80 11.15                                       SiO.sub.2                                                                         28.60                                                                              28.25                                                                              25.50                                                                              26.00                                                                              24.00                                                                              26.45                                                                              25.45                                       Al.sub.2 O.sub.3                                                                  --   --   --   --   --   --   --                                          Geo.sub.2                                                                         --   --   --   --   --   --   --                                          P.sub.2 O.sub.5                                                                   --   3.40 --   --   3.10 2.45 2.50                                        Li.sub.2 O                                                                        --   1.45 1.45 1.45 0.70 0.75 1.50                                        Na.sub.2 O                                                                        4.45 3.00 3.00 3.00 4.50 3.10 3.15                                        K.sub.2 O                                                                         6.70 4.50 4.50 4.50 4.55 7.00 4.75                                        MgO 3.85 3.90 5.95 4.40 2.90 6.00 7.15                                        CaO 15.20                                                                              14.90                                                                              16.65                                                                              15.05                                                                              16.30                                                                              15.30                                                                              14.20                                       SrO --   --   --   --   --   --   --                                          BaO --   --   --   --   --   --   --                                          ZnO --   --   1.00 --   --   2.00 --                                          PbO --   --   --   --   --   --   --                                          La.sub.2 O.sub.3                                                                  --   16.25                                                                              --   7.95 6.60 8.10 --                                          Y.sub.2 O.sub.3                                                                   14.85                                                                              --   3.70 --   --   --   --                                          Gd.sub.2 O.sub.3                                                                  --   --   3.00 --   --   --   --                                          Yb.sub.2 O.sub.3                                                                  --   --   --   --   --   --   9.20                                        TiO.sub.2                                                                         7.90 8.70 3.95 9.75 10.55                                                                              12.90                                                                              11.10                                       ZrO.sub.2                                                                         4.40 3.70 7.60 6.00 --   6.15 3.10                                        Nb.sub.2 O.sub.5                                                                  6.30 3.85 12.50                                                                              0.60 2.60 --   6.75                                        WO.sub.3                                                                          --   --   --   9.70 --   --   --                                          Ta.sub.2 O.sub.5                                                                  --   --   --   --   12.85                                                                              --   --                                          nd  1.7044                                                                             1.7056                                                                             1.7013                                                                             1.6981                                                                             1.7005                                                                             11.6990                                                                            1.6978                                      νd                                                                             40.0 41.2 40.5 39.0 37.9 38.10                                                                              37.8                                        S   3.18 3.27 3.19 3.22 3.26 3.12 3.16                                        __________________________________________________________________________                       22   23   24   25                                          __________________________________________________________________________                  B.sub.2 O.sub.3                                                                    6.90 12.65                                                                              11.25                                                                              11.40                                                     SiO.sub.2                                                                          18.60                                                                              26.30                                                                              21.10                                                                              23.65                                                     Al.sub.2 O.sub.3                                                                   --   --   --   --                                                        GeO.sub.2                                                                          --   --   6.35 --                                                        P.sub.2 O.sub.5                                                                    12.06                                                                              1.10 1.40 --                                                        Li.sub.2 O                                                                         2.22 2.30 1.45 1.45                                                      Na.sub.2 O                                                                         3.07 --   3.00 3.00                                                      K.sub.2 O                                                                          2.33 --   4.55 4.60                                                      MgO  6.99 6.15 5.90 6.95                                                      CaO  15.98                                                                              21.35                                                                              15.00                                                                              24.50                                                     SrO  --   --   --   --                                                        BaO  --   --   --   --                                                        ZnO  2.02 5.10 1.95 --                                                        PbO  --   --   --   --                                                        La.sub.2 O.sub.3                                                                   8.07 8.30 7.90 6.10                                                      Y.sub.2 O.sub.3                                                                    --   --   --   --                                                        Gd.sub.2 O.sub. 3                                                                  --   --   --   --                                                        Ab.sub.2 O.sub.3                                                                   --   --   --   --                                                        TiO.sub.2                                                                          7.92 5.10 7.75 6.30                                                      ZrO.sub.2                                                                          6.56 6.25 6.00 6.05                                                      Nb.sub.2 O.sub.5                                                                   6.45 5.40 6.40 6.00                                                      WO.sub.3                                                                           --   --   --   --                                                        Ta.sub.2 O.sub.5                                                                   --   --   --   --                                                        SnO  0.50                                                                     nd   1.7049                                                                             1.7052                                                                             1.7048                                                                             1.6995                                                    νd                                                                              39.2 42.1 39.1 41.0                                                      S    3.17 3.13 3.27 3.15                                        __________________________________________________________________________

The preceding examples can be repeated with similar success bysubstituting the generically or specifically described reactants and/oroperating conditions of this invention for those used in the precedingexamples. From the foregoing description, one skilled in the art caneasily ascertain the essential characteristics of this invention, andwithout departing from the spirit and scope thereof, can make variouschanges and modifications of the invention to adapt it to various usagesand conditions.

What is claimed is:
 1. An optical ophthalmic glass having an index ofrefraction of ≧1.69, an Abbe number of ≧37, and a density of ≦3.30g/cm³, consisting essentially of (in % by weight):

    ______________________________________                                        SiO.sub.2                  18-36                                              B.sub.2 O.sub.3            3-18                                               GeO.sub.2                  0-8                                                Al.sub.2 O.sub.3           0-6,                                               wherein SiO.sub.2 + B.sub.2 O.sub.3 + Al.sub.2 O.sub.3 + GeO.sub.2                                       25-39                                              P.sub.2 O.sub.5             0-14,                                             wherein SiO.sub.2 + B.sub.2 O.sub.3 + Al.sub.2 O.sub.3 + GeO.sub.2 +          P.sub.2 O.sub.5 =          30-44                                              Li.sub.2 O                 0-12                                               Na.sub.2 O                 0-14                                               K.sub.2 O                  0-18                                               Li.sub.2 O + Na.sub.2 O + K.sub.2 O =                                                                    2-18                                               MgO                        0-15                                               CaO                          7-21.35                                          MgO + CaO                  15-32                                              SrO                        0-13                                               BaO                        0-17                                               ZnO                        0-15                                               PbO                        0-10                                               SrO + BaO + ZnO + PbO      0-20                                               TiO.sub.2                  3.95-14                                            Nb.sub.2 O.sub.5           0-13                                               WO.sub.3                   0-10                                               TiO.sub.2 + Nb.sub.2 O.sub.5 + WO.sub.3 =                                                                10-21                                              ZrO.sub.2                  2.9-15,                                            La.sub.2 O.sub.3           0-20                                               Y.sub.2 O.sub.3            0-16                                               Gd.sub.2 O.sub.3           0-16                                               Yb.sub.2 O.sub.3           0-10                                               La.sub.2 O.sub.3 + Y.sub.2 O.sub.3 + Gd.sub.2 O.sub.3 + Yb.sub.2 O.sub.3      =                          0-20                                               Ta.sub.2 O.sub.5           0-13                                               HfO.sub.2                  0-6                                                SnO.sub.2                  0-6.                                               ______________________________________                                    


2. An optical and ophthalmic glass of claim 1 having an Abbe number of ≧39 and a density of ≦3.2 g/cm³, which is sufficiently stable withrespect to crystallization to permit continuous manufacture, and whichis acid resistant and resistant to climatic changes, consistingessentially of (% by weight):

    ______________________________________                                               B.sub.2 O.sub.3                                                                             5-14                                                            SiO.sub.2     24-32                                                           Al.sub.2 O.sub.3                                                                            0-6                                                             GeO.sub.2     0-8                                                             B.sub.2 O.sub.3 + SiO.sub.2 + Al.sub.2 O.sub.3 + GeO.sub.2 =                  33-39                                                                         P.sub.2 O.sub.5                                                                             0-6                                                             B.sub.2 O.sub.3 + SiO.sub.2 + Al.sub.2 O.sub.3 + GeO.sub.2 +                  P.sub.2 O.sub.5 = 37-43                                                       Li.sub.2 O    0-7                                                             Na.sub.2 O    0-8                                                             K.sub.2 O     0-11                                                            Li.sub.2 O + Na.sub.2 O + K.sub.2 O = 4-14                                    MgO           0-10                                                            CaO           12-21.35                                                        MgO + CaO = 18-27                                                             ZnO           0-8                                                             BaO           0-6                                                             SrO           0-5                                                             PbO           0-5                                                             ZnO + BaO + SrO + PbO = 0-8                                                   TiO.sub.2     6-10                                                            Nb.sub.2 O.sub.5                                                                            0-8                                                             WO.sub.3      0-10                                                            TiO.sub.2 + Nb.sub.2 O.sub.5 + WO.sub.3 = 13-19                               ZrO.sub.2     3-9                                                             La.sub.2 O.sub.3                                                                            0-11                                                            Y.sub.2 O.sub.3                                                                             0-12                                                            Gd.sub.2 O.sub.3                                                                            0-8                                                             Yb.sub.2 O.sub.3                                                                            0-7                                                             La.sub.2 O.sub.3 + Y.sub.2 O.sub.3 + Gd.sub.2 O.sub.3 + Yb.sub.2              O.sub.3 = 0-14                                                                Ta.sub.2 O    0-7                                                             HfO.sub.2     0-6                                                             SnO.sub.2     0-6                                                      ______________________________________                                    


3. A glass of claim 1 wherein the amount of TiO₂ is 6-10%.
 4. A glass ofclaim 1 wherein 0-1% of the oxygen ions are replaced by fluoride ions.5. A lens made of glass of claim 1 or
 2. 6. A lens of claim 5 foreyeglasses.
 7. A glass of claim 1 wherein the amount of TiO₂ is 6-14%.8. A glass of claim 1 wherein the amount of TiO₂ is 3.95-10%.
 9. A glassof claim 1 wherein the amount of ZrO₂ is 3-8%.
 10. A glass of claim 3wherein the amount of ZrO₂ is 3-8%.
 11. A glass of claim 7 wherein theamount of ZrO₂ is 3-8%.
 12. A glass of claim 1 wherein the amount ofZrO₂ is 3-15%.
 13. A glass of claim 3 wherein the amount of ZrO₂ is3-15%.
 14. A glass of claim 7 wherein the amount of ZrO₂ is 3-15%.